Dominik,
If the goal is fire resistance, see:
http://www.vansairforce.com/community/showthread.php?t=63633&highlight=ceramic&page=3
Dan Horton (DanH) outlines two methods that give good results in the burn test rig:
"For the cabin side, ceramic wool batting sealed in folded seam aluminum foil envelopes, with a mechanical attachment method. No glue please. Stainless foil is not necessary on the cabin side. All you need is HD [heavy duty] Reynolds Wrap [aluminum foil] from the grocery store.
For the engine side, ordinary Fiberfrax felt (available Wicks, Spruce, etc) under stainless steel foil, attached with SS pop rivets and sealed around the perimeter with 3M Firebarrier 2000. Common 24" wide SS foil is fine, actually preferred. Overlap a mid-panel seam about 2 inches and cover it with one strip of aluminum foil sticky tape. In a fire the aluminum tape will melt away instantly and provide a directed escape path for the outgassing binder in the Fiberfrax."-quote is from DanH's response to a similar question in the referenced thread.
Thicker is better, but there are weight tradeoffs. I plan to use 1/8" Fiberfrax.
Good luck,
Mike